Most burst brain aneurysms are smaller than a centimetre across
A brain aneurysm is a weak spot where an artery balloons outward. Many stay silent for life. When one tears, blood floods the space around the brain and brings on a thunderclap headache worse than any before it; about 60 percent of patients die immediately. Oddly, most ruptured aneurysms measure under 10 millimetres.
Also called cerebral aneurysms, these bulges can form anywhere in the brain but cluster on the ring of arteries at its base known as the Circle of Willis. Those in the posterior circulation are more prone to bursting. Doctors sort them by size, from small (under 15 millimetres) through large and giant to super-giant (above 50 millimetres), and by shape. Saccular or berry aneurysms, round pouches off one side of a vessel, are the most common. Fusiform ones widen an entire segment of artery and carry an estimated 1.6 to 1.9 percent yearly rupture risk. Tiny Charcot–Bouchard microaneurysms sit in vessels narrower than 300 micrometres, linked with long-standing high blood pressure.
Some arise from inherited connective tissue conditions, such as autosomal dominant polycystic kidney disease or hereditary haemorrhagic telangiectasia. Others are acquired: hypertension, smoking, alcoholism, obesity, cocaine and amphetamines, head injuries and infections of the artery wall are all associated. Coarctation of the aorta and arteriovenous malformations also raise the odds.
Rupture nearly always happens at the dome of the bulge, producing a subarachnoid haemorrhage. It usually strikes without warning, although small leaks sometimes cause sentinel headaches beforehand. A severe headache lasting hours to days, drowsiness, confusion, vomiting, vision trouble and collapse are typical. Complications include rebleeding, fluid build-up called hydrocephalus, and vasospasm, a narrowing of blood vessels that tends to appear within 21 days and shows on imaging in 60 percent of such patients. It is thought to follow the death of trapped inflammatory cells in the space around the brain.
Diagnosis uses CT or MR angiography, sometimes with a lumbar puncture to look for blood. Surgeons may clip the neck of the aneurysm or fill it with coils threaded through the blood vessels, both intended to stop further bleeding. Outlook depends on size, location, age and general health. Better scanners now catch many unruptured aneurysms by chance, which has spurred research into who needs treatment and into tools that predict rupture risk.
Source: Intracranial aneurysm
